(a) Field of the Invention
The present invention relates to a driving apparatus of a display device and a DC-DC converter.
(b) Description of the Related Art
Display devices used for monitors for computers and television sets include self-emitting displays such as light emitting diodes (LEDs), electroluminescence (EL) devices, vacuum fluorescent displays (VFDs), field emission displays (FEDs), and plasma panel displays (PDPs), and non-emitting displays such as liquid crystal displays (LCDs) requiring an external light source.
An LCD includes two panels provided with field-generating electrodes and a liquid crystal (LC) layer with dielectric anisotropy interposed therebetween. The field-generating electrodes are supplied with electric voltages and generate an electric field in the liquid crystal layer, and the transmittance of light passing through the panels varies depending on the strength of the applied field, which can be controlled by the applied voltages. Accordingly, desired images are obtained by adjusting the applied voltages.
The light may be emitted from a light source equipped in the LCD, or it may be natural light.
A lighting device for an LCD, i.e., a backlight unit, usually includes a plurality of fluorescent lamps such as external electrode fluorescent lamps (EEFLs) and cold cathode fluorescent lamps (CCFLs), or a plurality of light emitting diodes (LEDs), as light sources, which uniformly transmit the light to the entire front surface of the LC panels from the rear thereof.
When using the fluorescent lamps, characteristics of elements of the display device are deteriorated due to large power consumption and heating.
In addition, the fluorescent lamps have a stick shape, so they can easily break on impact. Moreover, since temperatures of the lamps vary in accordance with positions thereof, the luminance of the lamps also varies, the image quality of the LCD thereby decreases.
However, when LEDs are used, since each LED is a semiconductor device, the lifetime of the LED is long, the lighting speed of the LED is fast, and the power consumption is low. The LED also withstands impacts well and miniaturization thereof is easy.
Because of these benefits, LEDs have been equipped in monitors for middle or large sized LCDs such as for computers or television sets, as well as in small sized LCDs such as in mobile telephones, as a light source.
The LCD requires various DC (direct current) voltages for driving the LEDs, a cooling fan for cooling the LCD, and a plurality of microcomputers. Thus, the LCD includes a DC-DC converter that converts an AC (alternate current) voltage into a DC voltage and adjusts the voltage level of the DC voltage.
For obtaining a plurality of DC voltages, the LCD may include a plurality of DC-DC converters that generate DC voltages with the desired voltage levels, respectively, or may include a DC-DC converter having a transformer with a plurality of wound wire portions.
However, when multiple DC-DC converters are used, the volume and weight of the LCD are increased and the manufacturing cost is also increased. When a DC-DC converter having a transformer with a plurality of wound wire portions is used, the driving loss of the transformer is increased causing decrease in the efficiency of the DC-DC converter. Also because of the wound wire portions, the volume and weight of the LCD are increased.